server: fix type year has too many 0s in prepare/execute (#7525)

server/driver_tidb.go

@@ -391,7 +391,7 @@ func convertColumnInfo(fld *ast.ResultField) (ci *ColumnInfo) {
 			// Consider the decimal point.
 			ci.ColumnLength++
 		}
-	} else if fld.Column.Tp != mysql.TypeBit && fld.Column.Tp != mysql.TypeTiny {
+	} else if types.IsString(fld.Column.Tp) {
 		// Fix issue #4540.
 		// The flen is a hint, not a precise value, so most client will not use the value.
 		// But we found in rare MySQL client, like Navicat for MySQL(version before 12) will truncate

server/driver_tidb_test.go

@@ -88,4 +88,26 @@ func (ts tidbResultSetTestSuite) TestConvertColumnInfo(c *C) {
 	}
 	colInfo = convertColumnInfo(&resultField)
 	c.Assert(colInfo, DeepEquals, createColumnByTypeAndLen(mysql.TypeTiny, 1))
+
+	resultField = ast.ResultField{
+		Column: &model.ColumnInfo{
+			Name:   model.NewCIStr("a"),
+			ID:     0,
+			Offset: 0,
+			FieldType: types.FieldType{
+				Tp:      mysql.TypeYear,
+				Flag:    mysql.ZerofillFlag,
+				Flen:    4,
+				Decimal: 0,
+				Charset: charset.CharsetBin,
+				Collate: charset.CollationBin,
+			},
+			Comment: "column a is the first column in table dual",
+		},
+		ColumnAsName: model.NewCIStr("a"),
+		TableAsName:  model.NewCIStr("dual"),
+		DBName:       model.NewCIStr("test"),
+	}
+	colInfo = convertColumnInfo(&resultField)
+	c.Assert(colInfo.ColumnLength, Equals, uint32(4))
 }